Lots of pedal builders don't seem to understand how changing the value of the 1k resistor will alter the clipping from either the op amp or the diodes, so they tend to leave it the same as whatever pedal they are borrowing from. This is probably especially true if a pedal like the Klon is being copied.

If you can determine that the clipping diodes are indeed shunted to ground, and that the forward voltages are on the low side, like with the Klon, it would stand to reason that the gain pot simply varies between the clipped or bypassed signal paths, like with the Klon. Otherwise, you would need something pretty clever to not have buzzy distortion with a big volume drop as the gain goes up. To at least avoid the latter, you would need clipping diodes with a (combined) forward voltage of well over 1000 mV - it would probably be easier to just use LEDs.

Someone said that it's most likely a Baxandall tone circuit? That's usually not as hard to determine, because you'll have pairs of identical resistors or capacitors, and there's probably a chance that they are in proximity to the bass and treble pots.

I think that doing at least some of the above will at least give a better idea of what the Sick As either is or isn't.

"The Sick As Overdrive is a diversion from this well-worn path, taking its basic structure from the Klon Centaur® but with some major improvements for the modern player. The gain control serves a dual purpose— as the gain is increased, the ratio of gain-to-clean tone increases as well. This ensures that when the gain is rolled off, the tone never becomes muddy and unpleasant. You can control the amount of headroom and the character of the drive with the toggle switch. Choose from a more compressed, mid-range focused tone or an open, transparent, rhythm tone. The tone circuit is a powerful, two-band active EQ circuit capable of boosting or cutting the bass and treble frequencies up to 15dB for maximum versatility. The voltage is also boosted internally to 18V for increased clarity and headroom.

Here is said that it's a klone clone with some improvements... Diode clipping and bass control (Apparently it's a clone of the original pedal)[youtube]https://www.youtube.com/watch?v=Je-fQjrj9_o[/youtube]